Defrag your hard drive, but leave the SSD alone
From my limited tests, I’m firmly convinced that the tiny difference that even the best SSD defragger makes is not worth reducing the life span of your SSD. Add another voice to the chorus that’s singing “Don’t defrag your SSD.” If you’re truly convinced there are performance problems with your SSD due to file or cell fragmentation, get a utility that will issue a TRIM command. Or copy your data off, do a secure erase (using hdparm or Parted Magic), and copy it back again.

All four programs did a good job of optimizing hard drives, with PerfectDisk leading the way for one-off defragging, and both PerfectDisk and Diskeeper offering background defragging as you work. If you’re running a server or using programs that constantly write small files to disk, the background fragmentation prevention offered by Diskeeper and PerfectDisk could be useful. I saw no increase in performance on my PCs employing it, but it didn’t seem to slow down my PC, and more optimized writes can’t hurt.

If you don’t need the real-time features, check out the free version of UltimateDefrag for defragging entire disks intelligently and Piriform’s Defraggler for quickly defragging a single file or folder.